The present invention relates to weighing machines and is concerned in particular with control of vibratory feeders that dispense product from a bulk container to automated scales.
Vibratory feeders for dispensing product from bulk storage in a controlled stream are well known in the art and have been used before in weighing machines to load the product into a weigh scale. In most combination weighing machines, which operate in a cyclic manner, the vibratory feeders discharge into an accumulator located between the associated scale and the feeder, and the accumulator holds the product until the scale is dumped and ready to receive another charge of product.
It has been determined that in combination weighing machines, the target weight will be achieved or will be most closely approximated with highest probability when the number of dumped scales is approximately half or a third of the total number of scales searched. As the ratio of dumped scales to available scales goes up, the number of viable combinations goes down, and as the number of dumped scales goes down, the graduations of the combination weights become relatively coarse. Departure either way from the targeted number of dumped scales lowers the probability of accurately achieving the target weight. The targeted number can be controlled by causing the quantity or charge of product loaded into the scales to generally fall within the fractional part of the target weight which would permit about one half of the scales in the system to form the target weight.
Vibratory feeders for scales are not precision devices, and therefore, the quantity of product dispensed during a loading operation varies from one feed cycle to the next. Furthermore, in a machine having a plurality of scales, the feeders and the associated distribution system to the feeders from a bulk container may operate with different efficiencies and produce widely divergent charges.
It is accordingly a general object of the present invention to provide a vibratory feeder control that regulates the feeder operation and produces a charge or load in a scale that comes closer to a desired feed weight or allows a target weight to be produced with greater accuracy.